#include <fstream>
#include <climits>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int p5(int a)
{ int result=0;
  uint64_t p5=5;
  while(p5<=a)
  { result+=a/p5;
    p5*=5;
  }
  return result;
}

int main()
{ int p;
  fin>>p;
  int st=5*p,dr=INT64_MAX-1,mid,s;
  while(st<=dr)
  { mid=(st+dr)/2;
    if(p5(mid)==p)
    { 
      break;
    }
    if(p5(mid)>p)
    {
      dr =mid-1;
    }
    if(p5(mid)<p)
    {
      st=mid+1;
    }
  }
  s=mid-mid%5;
  fout<<s;
  return 0;
}